The physics most of us are familiar with is called Newtonian physics. You can use it to calculate how fast a ball will fall when dropped from the Eiffel tower, where a canon ball will land when shot at a particular angle and all kinds of other useful things. However, if you start dealing with things that are very small or very large, Newtonian physics is no longer accurate.
When dealing with very small things like computer processors, individual photos and other partials, you have to use Quantum Theory to produce meaningful results. When dealing with very large things, distances and objects, you have to use Einstein’s Theory of Relativity. With Newtonian physics, the GPS in your car would be impossible to build.
Most of the normal advice you read about productivity is like Newtonian physics. It is very useful for the normal things in our experience, but it is unusable if you are operating at the edges.
For example, most people believe that writing down all of the tasks you can think of is a good productivity practice and is part of GTD. This is true for most people working normal jobs. However, for people who are extremely productive, there is a fundamental shift in how they work. Keeping track of trivia would only distract them from their larger goals. Also, their accomplishment is based on picking the right things to do and not as much on doing as many tasks as possible.
When you are operating at the edges, be very careful what advice you follow. Just like Eistein had to come up with new theories to deal with very fast and very large objects, you will probably need to discover new (and sometimes unintuitive) rules that work for you.